1. Field of the Invention
The present invention relates generally to DC-DC electrical power oonverter circuits, and more specifically to DC-DC power converter circuits adapted for converting electrical energy received from a high-voltage, poorly regulated electrical power source to a well regulated lower voltage.
2. Description of the Prior Art
U.S. Pat. No. 5,999,417 entitled xe2x80x9cHigh Efficiency Power Converter,xe2x80x9d that issued Dec. 7, 1999, on a patent application filed by Martin F. Schlecht (xe2x80x9cthe ""417 patentxe2x80x9d), describes a DC-DC converter circuit adapted for converting electrical power received from a 48 volt direct current (xe2x80x9cVDCxe2x80x9d) power source to a 5 VDC output voltage for energizing the operation of computer digital logic circuits. As illustrated in FIG. 1 of the ""417 patent, the DC-DC converter disclosed there includes a regulation stage, an isolation stage, and control circuit that is coupled both to the regulation stage and to the isolation stage.
FIG. 2 of the ""417 patent depicts as the regulation stage a conventional voltage step-down converter circuit, a/k/a/ a buck converter circuit, which receives the 48 VDC battery voltage. Within the buck converter circuit, the 48 VDC battery voltage is applied across a capacitor, CIN, and from a first terminal of the 48 VDC battery to a switching transistor, QR. When the switching transistor, QR, turns-on, electrical current flows from the 48 VDC battery source through the switching transistor, QR, and through a series connected inductor L into the isolation stage of the DC-DC converter. During normal operation of the buck converter circuit when the switching transistor, QR, turns-off to block current from flowing from the 48 VDC battery source through the inductor L, electrical current continues to flow through the inductor L via a free-wheeling diode, DR, that connects between a second terminal of the 48 VDC battery source and a junction between the inductor L and the switching transistor, QR.
A version of the isolation stage of the DC-DC converter, illustrated in FIG. 2 of the ""417 patent, includes two, separate transformers T1 and T2. Each of the transformers T1 and T2 includes three windings: a primary winding T1PRI and T2PRI; a secondary winding T1SEC and T2SEC; and a tertiary winding T1TER and T2TER. The primary windings T1PRI and T2PRI of the transformers T1 and T2 are coupled to the inductor L of the regulator stage to receive electrical current therefrom, and are coupled respectively through MOSFETs Q1 and Q2 to the second terminal of the 48 VDC battery source. Connected in this way, while either of the transistors Q1 or Q2 are turned-on, the primary windings T1PRI and T2PRI of the transformers T1 and T2 are xe2x80x9ccurrent fedxe2x80x9d from the inductor L of the regulation stage. By this it is meant that the electrical current flowing into the primary windings T1PRI and T2PRI of the isolation stage transformers T1 and T2 is held relatively constant throughout a switching cycle of the DC-DC converter. It also means that voltage across the primary windings T1PRI and T2PRI of the isolation stage transformers T1 and T2 is free to have large, high frequency components.
During normal operation of the DC-DC converter, approximately one half of the switching cycle, transistor Q1 is turned-on and transistor Q2 is turned-off. While the transistor Q1 is turned-on, electrical current flows through the series connected inductor L and primary winding T1PRI of transformer T1. During a second half of the switching cycle, transistor Q2 is turned-on, and transistor Q1 is turned-off. While the transistor Q2 is turned-on, electrical current flows through the inductor L and through the primary winding T2PRI of the transformer T2 in the same manner as described above for transformer T1,
While the transistor Q1 is turned-on, a positive voltage is imposed across the primary winding T1PRI, and a magnetizing current flowing through the primary winding T1PRI increases. The voltage applied across the primary winding T1PRI and the current flowing therethrough induce a corresponding flow of electrical current (transformed by the turns ratio between the primary winding T1PRI and the secondary winding T1SEC) through the secondary winding T1SEC of the transformer T1, and through a diode D1 connected in series with the secondary winding T1SEC both to an output filter capacitor COUT and to a load that is coupled to the isolation stage. When the transistor Q1 turns-off thereby blocking an electrical current from flowing through the primary winding T1PRI, the voltages across the windings T1PRI, T1SEC and T1TER reverse thereby causing electrical current to flow through the tertiary winding T1TER of the transformer T1 and a diode D3 connected in series with the tertiary winding T1TER to the output filter capacitor COUT and the load. Electrical current flowing through the tertiary winding T1TER of the transformer T1 provides a means to reset the core of the transformer T1, and to recover most of the magnetizing inductance energy stored in the core while the transistor Q1 is turned-on. Since as described above the transistors Q1 and Q2 operate out of phase, the transformer T2 operates similar to but out of phase with the transformer T1 for supplying electrical currents respectively through the secondary winding T2SEC and a diode D2, and the tertiary winding T2TER and a diode D4 to the output filter capacitor COUT and the load.
The control circuit illustrated in FIG. 1 of the ""417 patent provides drive signals to control terminals of the transistors QR, Q1 and Q2 illustrated in FIG. 2. The ""417 patent explains that the separate regulation stage, which in the illustration of FIG. 1 is on the primary side of the converter""s isolation stage, regulates operation of the DC-DC converter. In this particular configuration, regulation is effected by controlling the duty cycle of the transistor QR in response to one or more parameters sensed in the control circuit, which may be sensed on the primary side of the converter""s isolation stage.
A significant fraction of the energy dissipated in a DC-DC converter such as that depicted in FIG. 2 of the ""417 patent occurs in the diodes D1, D2, D3 and D4, particularly if the load and/or source voltages are low, e.g. 3.3, 5, or 12 volts. To reduce this rectification conduction power loss, the diodes D1, D2, D3 and D4 may be replaced with transistors which have an on-state voltage that is much less than the conduction voltage drop of the diodes D1, D2, D3 and D4. Transistors used in this way are frequently called synchronous rectifiers, and are typically power MOSFETs for DC-DC converters switching in the 100 kHz and higher range.
FIGS. 3, 5, 6A, 6B and 7-9 of the ""417 patent illustrates an isolation stage for the DC-DC converter in which a pair of N-channel MOSFET synchronous rectifiers Q3 and Q4 replace the diodes D1, D2, D3 and D4. The positions of these synchronous rectifiers Q3 and Q4 in the circuit differs slightly from the positions of the diodes D1, D2, D3 and D4 in FIG. 2. The synchronous rectifiers Q3 and Q4 still connect in series with the respective secondary winding T1SEC and T2SEC, but drains of the N-channel MOSFET synchronous rectifiers Q3 and Q4 connect to the negative output terminal of the respective secondary windings T1SEC and T2SEC rather than to the positive output terminal. The synchronous rectifiers Q3 and Q4 connect in this way to the respective secondary winding T1SEC and T2SEC so source terminals of both N-channel MOSFET synchronous rectifiers Q3 and Q4 connect to a single, common DC node, i.e. circuit ground.
If instead of N-channel MOSFETS, P-channel MOSFETs were used for the synchronous rectifiers Q3 and Q4, their respective drain terminals would connect to the positive output terminals of the respective secondary winding T1SEC and T2SEC as shown in the partial schematic of FIG. 4 in the ""417 patent. The configuration for the P-channel MOSFETS synchronous rectifiers Q3 and Q4 shown in FIG. 4 permit connecting the source terminals of the synchronous rectifiers Q3 and Q4 to a single, common DC node.
As shown in FIGS. 3, 4, 5, 6A, 6B and 7-9, the gates of the MOSFET synchronous rectifiers Q3 and Q4, which drains are connected respectively to the secondary winding T1SEC and T2SEC, are cross-coupled to the secondary winding T2SEC and T1SEC of the opposite transformers T2 and T1. Coupled in this way, the voltage across one transformer determines the gate voltage for the opposite MOSFET synchronous rectifier, and therefore the conduction state (on or off) of the MOSFET synchronous rectifier connected to the other transformer. This configuration for the MOSFET synchronous rectifiers inherently applies properly timed driving signals to the gates of the MOSFET synchronous rectifiers without requiring any special control circuitry on the secondary side of the transformers T1 and T2.
Frequently, operation of telecommunication systems is energized by relatively high-voltage battery power supplies, e.g. 48 VDC that at times may exhibit a poorly regulated output voltage. During re-charging of these high-voltage batteries, the voltage of this power source may increase to 75 VDC for extended intervals of time, with intermittent voltage spikes reaching 100 VDC. However, the equipment energized by a DC-DC converter such as that disclosed in the ""417 patent must operate continuously and reliably while the high-voltage batteries are being recharged. Thus, there exists a need for a cost-effective DC-DC converter, capable of being energized by electrical power drawn from a poorly regulated power supply, that is also capable of supplying well-regulated electrical power to equipment at a much lower voltage, e.g. 1.0-3.0 VDC, at relatively high currents, e.g. up to 60 amperes (xe2x80x9cAMPsxe2x80x9d).
While use of high-voltage integrated circuit technology permits building a DC-DC converter having characteristics such as those outlined above, such an approach possesses several disadvantages. First, building high-voltage integrated circuits requires specialized integrated circuit manufacturing technology. A significant disadvantage of high-voltage integrated circuits made using such specialized manufacturing technology is that the integrated circuits switch slowly which increases power loss within the DC-DC converter. Moreover, high-voltage integrated circuits occupy a larger area of silicon than low-voltage integrated circuits which further increases the integrated circuits"" cost.
An object of the present invention is to provide DC-DC converter that can be energized by a poorly regulated power supply and that can supply well-regulated electrical power.
Another object of the present invention is to provide DC-DC converter that can be energized by a poorly regulated, comparatively high-voltage power supply and that can supply well-regulated electrical power at a much lower voltage, and at a high current.
Another object of the present invention is to provide a cost-effective DC-DC converter that can be energized by a poorly regulated power supply and that can supply well-regulated electrical power.
Another object of the present invention is to provide DC-DC converter using only low-voltage integrated circuit technology that can be energized by a poorly regulated, comparatively high-voltage power supply and that can supply well-regulated electrical power at a much lower voltage, and at a high current.
Briefly, the present invention is a DC-DC converter adapted for converting direct current (xe2x80x9cDCxe2x80x9d) electrical power received from first and second output terminals of a high-voltage DC power supply. The DC-DC converter is preferably adapted for supplies DC electrical power to a load at a well-regulated output voltage that is significantly lower than the voltage which the DC-DC converter receives from the high-voltage DC power supply.
The DC-DC converter includes a regulated voltage-reduction stage which receives DC electrical power from the output terminals of the high-voltage DC power supply, and supplies DC electrical power from an output at a voltage which is lower than that received from the high-voltage DC power supply. The voltage-reduction stage includes a voltage-reduction electronic switch for alternatively:
1. electrically coupling the first output terminal of the high-voltage DC power supply to the output of the voltage-reduction stage; and
2. electrically de-coupling the first output terminal of the high-voltage DC power supply from the output of the voltage-reduction stage.
The voltage-reduction stage also includes a low-voltage, voltage-reduction integrated circuit (xe2x80x9cICxe2x80x9d) that is energized by DC electrical power received from the output terminals of the high-voltage DC power supply. The voltage-reduction IC supplying an electrical signal to the voltage-reduction electronic switch which controls alternative electrical coupling and de-coupling effected by the voltage-reduction electronic switch. The voltage-reduction stage also includes a voltage-reduction current source that is coupled to the voltage-reduction IC to effect a controlled flow of electrical current between the output terminals of the high-voltage DC power supply through the voltage-reduction IC and the voltage-reduction current source.
The DC-DC converter also includes a separately regulated isolation stage adapted for supplying DC electrical power to the load at the output voltage that is significantly lower than the voltage which the DC-DC converter receives from the high-voltage DC power supply. The regulated isolation stage includes an isolation transformer having a primary winding that receives DC electrical power from the output of the voltage-reduction stage. The isolation transformer also has a secondary winding that is magnetically coupled to the primary winding. The regulated isolation stage includes also includes at least one transformer electronic switch connected to the primary winding of the isolation transformer. The transformer electronic switch alternatively:
1. permits electrical current to flow between the output of the voltage-reduction stage through the primary winding of the isolation transformer and the transformer electronic switch to the second output terminal of the high-voltage DC power supply; and
2. blocks the flow of electrical current between the output of the voltage-reduction stage through the primary winding of the isolation transformer and the transformer electronic switch to the second output terminal of the high-voltage DC power supply.
This operation of the transformer electronic switch induces an alternating current (xe2x80x9cACxe2x80x9d) in the secondary winding of the isolation transformer.
The regulated isolation stage also includes a rectifier circuit coupled to the secondary winding of the isolation transformer. The rectifier circuit rectifies the AC received from the secondary winding to produce therefrom DC electrical power which the DC-DC converter is adapted for supplying to the load. An output-voltage sensor, included in the regulated isolation stage, produces an output signal which is responsive to the output voltage supplied to the load.
A low-voltage, isolation-stage IC, included in the regulated isolation stage, is energized by DC electrical power received from the output terminals of the high-voltage DC power supply. The isolation-stage IC receives the output signal produced by the output-voltage sensor and supplies an electrical signal to the transformer electronic switch for controlling the alternative electrical coupling and de-coupling effected by the transformer electronic switch. The isolation-stage IC produces this electrical signal responsive to the output signal received from the output-voltage sensor. An isolation-stage current source included in the regulated isolation stage, is coupled to the isolation-stage IC to effect a controlled flow of electrical current between the output terminals of the high-voltage DC power supply through the voltage-reduction IC and the voltage-reduction current source.
A reduction-stage feedback circuit couples an output signal produced by the isolation-stage IC to the voltage-reduction IC to control the electrical signal which the voltage-reduction IC supplies to the voltage-reduction electronic switch.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.